This invention relates to benzothiophenes, particularly 3-hydroxybenzothiophenes having the unusual 2-enamido side chains, such as those of Formula I: ##STR2##
Compounds of formula I have been found to be effective inhibitors of both cyclooxygenase and lipoxygenase and are thereby useful in the treatment of pain, fever, inflammation, arthritic conditions, asthma, allergic disorders, skin diseases, cardiovascular disorders, psoriasis, inflammatory bowel disease, glaucoma or other prostaglandins and/or leukotriene mediated diseases. Furthermore, these compounds have been found to exhibit cytoprotective activity which does not involve the inhibition of gastric acid secretion but can be used at relatively low dosages for increasing the resistance of gastro-intestinal mucosa to strong irritants.
Among various potent biological mediators derived from the oxygenation of arachidonic acid, prostaglandins and leukotrienes have been linked to various diseases. Notably, the biosynthesis of prostaglandins has been identified as a cause of inflammation, arthritic conditions (e.g., rheumatoid arthritis, osteoarthritis and gout), psoriasis, inflammatory bowel disease, and pain. Furthermore, the formation of leukotrienes has been connected to immediate hypersensitivity reactions and pro-inflammatory effects. It has been established that arachidonic acid undergoes oxygenation via two major enzymatic pathways:
(1) The pathway catalyzed by the enzyme cyclooxygenase; and PA1 (2) The pathway catalyzed by the enzyme 5-lipoxygenase. PA1 R is PA1 R.sup.1, R.sup.2 and R.sup.3 independently are PA1 R.sup.4 is PA1 R.sup.2 and R.sup.3 independently are: PA1 R.sup.4 is H or --CH.dbd.CHR.sup.2.
Interruption of these pathways by enzyme inhibition has been explored for effective therapy. For example, non-steroidal anti-inflammatory drugs (NSAID) such as aspirin, indomethacin and diflunisal are known cyclooxygenase inhibitors which inhibit the process wherein arachidonic acid is oxygenated via cyclooxygenase to prostaglandins and thromboxanes.
Recently, it has been observed that certain leukotrienes are responsible for diseases related to immediate hypersensitivity reactions such as human asthma, allergic disorders, and skin diseases. In addition, certain leukotrienes and derivatives thereof are believed to play an important role in causing inflammation (B. Samuelsson, Science, 220, 568 (1983); D. Bailey et al, Ann. Rpts. Med. Chem., 17, 203 (1982)).
Conditions involving elevated intraocular pressures which are too high for normal function may result in irreversible loss of visual function. For example, glaucoma, if untreated, may eventually lead to blindness. Ocular hypertension, i.e., the condition of elevated intraocular pressure without optic nerve head damage or characteristic glaucomatous visual field defects, is now believed by many ophthalmologists to represent the earliest phase of glaucoma.
Many of the drugs formerly used to treat glaucoma proved not entirely satisfactory. Indeed, few advances were made in the treatment of glaucoma since pilocarpine and physostigmine were introduced. Only recently have clinicians noted that many .beta.-adrenergic blocking agents are effective in reducing intraocular pressure. While many of these agents are effective in reducing intraocular pressure, they also have other characteristics, e.g. membrane stabilizing activity, that are not acceptable for chronic ocular use.
To be an effective and acceptable topical agent, for treating inflammation in the eye, or ocular hypertension related diseases such as glaucoma, the drug must not only penetrate the ophthalmic tissues to reach the active sites within the eye, but it must also be devoid of those side effects including irritation, allergic reaction and the like which would militate against long term administration.
With respect to the cytoprotective activity of the compounds of the present invention, it has been known that (1) gastric cytoprotection does not involve inhibition of gastric acid secretion. For example, protaglandin F2B does not inhibit gastric acid secretion, but it does induce gastric cytoprotection (S. Szabo et al., Experimentia, 38, 254, 1982); (2) lower effective dosages of cytoprotective agents are required than that of gastric acid inhibitors; and (3) the cytoprotective activity of a compound may be observed in both animals and man by noting the increased resistance of gastrointestinal mucosa to strong irritants. For example, animal studies have shown that cytoprotective compounds will prevent gastric lesions induced by oral administration of strong acids, strong bases, ethanol, hypertonic saline, etc.